I'm interested in launching a window in a temporary session, like how UAC prompts appear. There's been some interest in this concept from a few people, so I figured I'd ask here. Essentially what we're going for is an elevated window like the UAC "are you sure you want to <...>" prompts, but with an arbitrary window. The end goal is to prevent window event hooks and all sorts of other issues that might occur during password entry.
I've had a quick look at the UAC APIs and a few other places, but there's nothing particularly useful out there. Obviously the UAC prompts get elevated to their own desktop session somehow, so there must be a way to create windows in such a way.
You can create a desktop using CreateDesktop. You can use SwitchDesktop to switch to the new desktop. Then you can call SetThreadDesktop on your main thread and draw your window. To get back get the handle of the default desktop by calling OpenDesktop with "Default" as lpszDesktop and use SwitchDesktop with this handle. You can also run Processes on a certain desktop. In order to do this you have to set lpDesktop member of the STARTUPINFO structure to the name of the desktop the process should be run on. Close the handles to the desktops after using them (CloseDesktop).
You can show your own window on an own desktop in this way.
The secure desktop used by UAC and by the Logon UI is called "Winlogon". In order to access it you need system rights. Luke provided an example in one of his answers.
Brian R. Bondy wrote a blog entry on desktops and window stations which is worth reading.
